In communications systems, it is often desirable to be able to distinguish between legitimate control or data signals and noise signals which possess some of the same characteristics as the legitimate data or control signals. In the particular case of a telephone communications system where such data and control signals are in the audible range, it is necessary to discriminate against noise signals appearing on a pair of telephone lines, which noise signals may be formed in one instance by human voices and hereinafter referred to as voice signals.
The prior art demonstrates many techniques and apparatus for detecting legitimate data and control signals and for rejecting noise signals. Such techniques and apparatus generally inhibit the operation of associated equipment from receiving and acting upon the noise signals until such time as legitimate data and control signals are received.
The present invention is an improvement on the prior art in that it positively inhibits the operation of associated equipment when noise signals are received, even though those noise signals may have certain characteristics which are common with legitimate data or control signals.
Therefore, it is an object of this invention to provide an apparatus for detecting voice and other noise signals present on telephone or similar communications lines.
It is a further object of this invention to provide such an apparatus which inhibits the production of an output signal therefrom within a very short period of time following the first occurrence of such voice or other noise signals on the lines.
It is still a further object of this invention to provide an apparatus which does not respond to voice and other noise signals which may have one characteristic which is common with legitimate data and control signals appearing on a communications line.
It is yet a further object of this invention to provide such an apparatus which responds only to legitimate data and control signals on the lines.